JSF ViewHandlerWrapper causes NullPointerException

I have a little issue with a JSF ViewHandlerWrapper that I've coded. It works fine most of the times, but at times I will get a NullPointerException from the very core of Mojarra and thus started to wonder whet开发者_开发知识库her I implemented my ViewHandlerWrapper correctly.

public class TokenViewHandler extends ViewHandlerWrapper {
    private ViewHandler parent;

    public TokenViewHandler(ViewHandler parent) {
        this.parent = parent;
    }

    @Override
    public ViewHandler getWrapped() {
        return parent;
    }

    @Override
    public void renderView(FacesContext context, UIViewRoot viewToRender) throws IOException, FacesException {
        final String token = UUID.randomUUID().toString();

        findAndModifyForms(viewToRender, token, context);

        getWrapped().renderView(context, viewToRender);
    }

    private void findAndModifyForms(final UIComponent component, final String token, final FacesContext ctx) {
        if (component instanceof UIForm) {
            final HtmlInputHidden hidden = (HtmlInputHidden) ctx.getApplication().createComponent(HtmlInputHidden.COMPONENT_TYPE);
            hidden.setValue(token);
            component.getChildren().add(hidden);
        } else {
            for (UIComponent tempComponent : component.getChildren()) {
                findAndModifyForms(tempComponent, token, ctx);
            }
        }
    }
}

From the code you quickly realize that I want to add a inputHidden-component with a UUID value to each form on the view.

As I haven't found any good examples for ViewHandlerWrappers I assumed that it should look like a ExceptionHandlerWrapper but since I get the occassional NPE using my ViewHandler, I assume that something is wrong and I can't seem to see it.

This seems to be related to a bug in partial state saving, see issue 1414.

The IceFaces guys encountered a similar problem and they got it (temporarily) fixed by adding the following line:

facesContext.getViewRoot().addComponentResource(facesContext, new UIOutput(), "head");

Give it a try. Do it before rendering the view.